1. Field of the Invention
The present invention relates to an image recording apparatus and an image recording method, and more particularly to an image recording apparatus and an image recording method that correct density unevenness caused by variation in characteristics of recording elements when an image is recorded on a recording medium by using a recording head including a plurality of recording elements.
2. Description of the Related Art
In an image recording apparatus such as inkjet recording apparatus equipped with a plurality of nozzles, variation occurs in ejection characteristics among the nozzles with the passage of time because the ink dries in the nozzle opening, thereby producing deteriorated nozzles in which ejection of ink is adversely affected or non-ejecting nozzles that cannot eject the ink at all. The presence of such deteriorated nozzles and non-ejecting nozzles leads to permanent disturbance of recorded images, such as white streaks, and is therefore undesirable. Accordingly, Japanese Patent Application Publication No. 2003-136764 suggests a technique for preventing the disturbance of recorded image caused by deterioration of nozzle ejection capability.
Japanese Patent Application Publication No. 2003-136764 discloses an inkjet recording apparatus that records an image on a recording medium by ejecting ink from a plurality of nozzles. In such an inkjet recording apparatus, a pattern (shading pattern and non-ejection detection pattern) for measuring recording characteristics of a recording head is outputted, the density of the pattern is measured, and a non-ejecting nozzle that is in a non-ejection state is specified on the basis of the measurement results. Further, a density distribution corresponding to each nozzle is obtained and convolution integration using VTF (Visual Transfer Function) or PSF (Point Spread Function) is performed with respect to the density distribution. The result relating to the portion of the obtained density distribution that corresponds to the non-ejecting nozzle is compared with a reference set value that has been set in advance, and a complementary table for complementing with a color different from the color of the ink ejected by the non-ejecting nozzle is determined for each nozzle on the basis of the comparison results. Image data corresponding to the non-ejecting nozzle are converted into ink ejection information of different color that is ejected from another nozzle on the basis of the complementary table determined in the above-described manner.
Thus, with the technique disclosed in Japanese Patent Application Publication No. 2003-136764, non-ejection information is acquired on the basis of the recording pattern and complementary processing with an ink of different color is performed when a target nozzle is a non-ejecting nozzle. Where the target nozzle is not a non-ejecting nozzle, the amount of ink ejected from the target nozzle is adjusted, thereby performing a shading correction processing of correcting the density unevenness. With the technique disclosed in Japanese Patent Application Publication No. 2003-136764, it is possible to determine whether the non-ejection complementary processing or the shading correction processing is to be used, on the basis of the non-ejection information.
However, the range of levels of density unevenness caused by deterioration of nozzle ejection performance is wide, and in some cases, it is actually extremely difficult to cope with density unevenness by using only the usual shading correction processing with respect to deteriorated nozzles that have lost the capability of ejecting the original ink density (ink amount).
In particular, with the technique disclosed in Japanese Patent Application Publication No. 2003-136764, the usual shading correction processing is implemented even when the target nozzle is a nozzle (referred to hereinbelow as “abnormal density nozzle”) that cannot eject ink of sufficient density even after the shading correction density but is not detected as a non-ejecting nozzle. However, density unevenness caused by the presence of such an abnormal density nozzle is not appropriately improved even by the density-increasing density processing (shading correction processing) that increases the amount of ink ejected from the abnormal density nozzle. As a result, the disturbance of image quality cannot be sufficiently prevented.
Furthermore, with the technique disclosed in Japanese Patent Application Publication No. 2003-136764, complementary processing of a non-ejecting nozzle is performed by inks of different colors. Therefore, the complementation ability is greatly affected by the types and number of inks of different colors that are used for the complementary processing. However, in the usual inkjet recording apparatus, a limitation is placed on the types and number of inks that can be used. As a result, the complementary processing of a non-ejecting nozzle sometimes cannot be sufficiently advanced. In addition, with the technique described in Japanese Patent Application Publication No. 2003-136764, shading data for the same color are also computed for the non-ejecting nozzle portion, but because of the non-ejection state, these data are actually not outputted and therefore the non-ejection complementation is performed by ink of different color.